Preparations for the terrestrial digital broadcasting method ISDB-T (Integrated Services Digital Broadcasting—Terrestrial) are proceeding as Japan's terrestrial television broadcasting faces the end of terrestrial analogue broadcasts, scheduled for July 2011.
Recently, small-scale transmission output relay stations in particular are being prepared in every region of the country. In terrestrial digital broadcasting, it has become possible to send broadcast signals of the same content on the same frequency from a plurality of relay stations, known as the SFN (Single Frequency Network) method, as a result of the introduction of a guard interval structure where the OFDM modulation method is applied. Also in terrestrial digital broadcasting, relay station networks are being constructed that use the SFN method together with the MFN (Multi Frequency Network) method where the physical channel changes with each relay station.
In this environment, moving vehicles receiving terrestrial digital broadcasts while moving will need to set up the receiving channel again when leaving the broadcasting area that applies to the broadcast currently being viewed, and entering the broadcasting area of a new relay station.
FIG. 30 is a block diagram showing the structure of a conventional first digital broadcast receiver (for example, refer to Patent Literature 1).
The digital broadcast receiver 5100 shown in FIG. 30 includes (i) a first front end unit 5101 which outputs packet data of a first TS (Transport Stream) after having acquired a received digital broadcast and performed demodulation, (ii) a second front end unit 5102 which outputs packet data of a second TS after having acquired a digital broadcast of a frequency that is different from the signal acquired by the first front end unit 5101, and after having performed demodulation, (iii) a TS selector unit 5103 which selects and outputs one of either the first TS packet data or the second TS packet data, (iv) a data separating unit 5104 which separates a predetermined signal from the output of the TS selector unit 5103, (v) a decoder unit 5105 which decodes and outputs the fixed signal separated by the data separating unit 5104, and (vi) a reception stability judgment unit 5106 which judges the reception stability of the first front end unit 5101 and the second front end unit 5102 based on the reception status information outputted from the first front end unit 5101 and the second front end unit 5102 and the tuning status information outputted from the data separating unit 5104.
The TS selector unit 5103 selects by TS packet unit one of either the first TS packet data group or the second TS packet data group based on the judgment results of the reception stability judgment unit 5106, and outputs the data.
The conventional first digital broadcast receiver 5100 has two systems of digital broadcast front end units, and when receiving signals at a location where a plurality of transmission station (relay station) broadcast areas overlap, one of the front end units is used to receive and demodulate signals sent from one of the transmitting stations, and the other front end unit is used to receive and demodulate signals sent by a different frequency. Then, the digital broadcast receiver 5100 extracts tuning information from within the TS packet data acquired from the respective front end units, and selects for output by packet unit, one of the TS packet data groups outputted from both front end units, in accordance with the separately generated reception stability judgment results. In this way, a digital broadcast receiver is proposed which receives and demodulates broadcasts of the same content with different receiving frequencies and selects the demodulated signal for use.
Also, FIG. 31 is a block diagram showing the structure of a conventional second digital broadcast receiver (for example, refer to Patent Literature 2). The conventional second digital broadcast receiver 5200 shown in FIG. 31 includes a first antenna 5201, a second antenna 5202, a first tuner 5203, a second 5204, a first demodulation unit 5205, a second demodulation unit 5206, a first coefficient setting unit 5207, a second coefficient setting unit 5208, a signal synthesis unit 5209 and a control unit 5210.
When setting up the digital broadcast receiver 5200, the first tuner 5203 and the second tuner 5204, being controlled by the control unit 5210, change the reception channel and perform a scan process of relay stations from which reception is possible. When the scan has been completed, the control unit 5210 changes the reception channel of the second tuner 5204 to the frequency of the channel which is sending the same broadcast as that of the broadcast program which the first tuner 5203 is tuned in to. The first demodulation unit 5205 and the second demodulation unit 5206, after receiving and demodulating a signal from both the first tuner 5203 and second tuner 5204, output the demodulation signals to both of the first coefficient setting unit 5207 and second coefficient setting unit 5208. The first coefficient setting unit 5207 and second coefficient setting unit 5208, after multiplying the weighted coefficient indicated by the control unit 5210 by the demodulation signals, output the demodulation signals to the signal synthesis unit 5209. The signal synthesis unit 5209 adds the post-weighting demodulation signals that have been outputted from the first coefficient setting unit 5207 and second coefficient setting unit 5208, and outputs the result to the subsequent decoding unit of the digital broadcast receiver 5200.
The conventional second digital broadcast receiver 5200, as is described above, has two systems of digital broadcast demodulation units, and when in an area where a same broadcast program is sent from a first relay station and second relay station on channels with different frequencies, the second digital broadcast receiver 5200 receives signals from both the first relay station and second relay station together, and actualizes diversity reception in view of the reception state of the broadcasting from the first and second relay stations.